1. Field of the Invention
The present invention relates to a process for producing a composite raw material for ceramics which is uniformly mixed and useful as the raw material for the production of a composite material for ceramics and to a composite raw material for ceramics which is produced by the above-mentioned process.
2. Description of the Prior Art
A composite material for ceramics which comprises at least two types of raw material components uniformly mixed with each other is produced by firing a composite raw material for ceramics which is prepared by mixing at least two raw materials for ceramics.
The ball mill process for producing a composite raw material for ceramics comprises dispersing at least two types of raw materials to be mixed in a liquid medium in a pot to form a slurry and mixing the raw materials in the slurry form together with grinding balls is widely employed because of its simplicity and convenience.
In the usual ball mill process, solid matters are separated by filtration or other means from the slurry in which the raw materials are dispersed and compounded to recover the composite raw material. In the aforesaid process, however, when there is considerable difference between the raw materials to be used in terms of density, particle size, shape, etc., it brings about a difference in the dispersion characteristics and/or sedimentation velocity of the particles in the liquid medium and thus the problem that the raw material components that have once been well mixed are reseparated during the operation of separation or recovery, thereby making it difficult to produce uniformly mixed composite raw material.
In order to solve the above-mentioned problem, there have been developed a spray drying method in which the slurry containing raw material components dispersed and mixed therein is spray dried to recover the composite raw material, a method for recovering the composite raw materials by drying the slurry with a fluidized dryer and like methods. The aforesaid methods, however, suffer from the disadvantage in that the yield of the composite raw materials and thermal efficiency are low; and besides the equipment to be used in these methods is expensive, thus causing practical problems. Such an obstacle in the technological development on the production of composite raw materials is one of the contributors to the obstruction to the development of composite ceramics materials and industrial utilization thereof.
Surprisingly, it has been found that when aluminum hydroxide is precipitated in the slurry in which at least two types of raw material components are present in uniformly dispersed and mixed state, these components coagulate and precipitate together with the precipitate of aluminum hydroxide, while retaining the uniformly mixed state.